I have not tried this Modify Flat-hop.
I did just get in the Prommy Retension Nubs and a replacement FireFly Buffer Rubber.
I went back and forth over the last few months whether to buy these or not.
Home made nubs are just as good, and often better.

One thing I really like about the Modify from what I see is the fact the Nub has no ailerons(downward wings/flaps).
This is better for KWA Hop-up unit in my opinion, but not everyone shares the same opinion.

Either way, you should definitely try the flat-hop if you have not.
Give this Modify one a try. Let us know how it turns out.

ok i got this in today and tried it out real quick on my EDGI 425 barrel in my MOD1.....

well... it was super duper ultra tight trying to get that bad boy in the hop up.. but it did go in.

didnt work worth crap with the modify nub... just couldnt get it to adjust down far enough to give me as much flat nub in there as i had with my factory bumper.. just seemed like the modify nub was too small....

air seal seamed to be ok & i'll just try it in another gun later on....

ok i got this in today and tried it out real quick on my EDGI 425 barrel in my MOD1.....
well... it was super duper ultra tight trying to get that bad boy in the hop up.. but it did go in.
didnt work worth crap with the modify nub... just couldnt get it to adjust down far enough to give me as much flat nub in there as i had with my factory bumper.. just seemed like the modify nub was too small....
air seal seamed to be ok & i'll just try it in another gun later on....
put the r/cccp hop set up back in it & went from there.

Try a Super Nub.
A Super Nub is a great performing, cheap alternative to after-market Flat-Nubs out there.

- Apply a tiny drop of Super Glue to the unmodified Nub.This is your Base-Nub.
Over-lap the unmodified Nub with the Nub you you just cut(Over-lapping Nub).
You will need to stabilize the Base-Nub as you over-lapping it mwith the second Nub.
I place the Base-Nub on a pick and just lay the pick flat on a table to do this.

-Add Nub Mod (Optional)

- Install into Hop-up unit.
Make sure the Over-lapping Nub is on top.
This is the one that will be making contact with the Bucking.

Also note that it is not just the nub that is different in this device, the inside of the bucking does not have any protrusion for the nub (part put on the hop up arm) to push into the bb. This is the flat hop bucking.

I have one and I am going to put it on a barrel with the r-hop patch and a legit M-nub.

Also note that any bucking, except the 2gx KWA bucking, is going to be really tight in a KWA hop up.

I buy this a month ago........same result of sdk1968, but I work with the modify nub and make them a super nub, and work better, with a madbull 6.01 455 on a standar SR10, I can measure 200 feet of distance with 8 of 10 accuracy on foot with 0.25 bb's.
Better result with a flat hoped KWA bucking and the same nub, 10 of 10 on 200" and 8 of 10 on 220".

Also note that it is not just the nub that is different in this device, the inside of the bucking does not have any protrusion for the nub (part put on the hop up arm) to push into the bb. This is the flat hop bucking.

I have one and I am going to put it on a barrel with the r-hop patch and a legit M-nub.

Also note that any bucking, except the 2gx KWA bucking, is going to be really tight in a KWA hop up.